1. Field of the Invention
The present invention relates to a package for a resin-shield type semiconductor device, particularly a premold type semiconductor package, and a process for producting the same.
2. Description of the Related Art
In general, the resin-shield type semiconductor device is produced by mounting a semiconductor chip in a chip-mounting area of a lead frame, then electrically connecting the semiconductor chip to leads by wires, and thereafter, shielding the semiconductor chip with resin.
Alternatively, there is a so-called premold type package wherein a molded body having a recessed chip-mounting area is preliminarily formed by an insert molding of a lead frame. According to this package, a semiconductor chip is mounted in the chip-mounting area, then circuit patterns around the chip-mounting area are electrically connected to the semiconductor chip, and thereafter, the chip-mounting area is covered with a lid, resulting in a semiconductor device.
Nowadays, the latter package of a simple structure has been widely employed in various uses because it is improved in air-tightness due to the advancement of a passivation film on the semiconductor chip itself and/or an adhesive for sealing between the lid and the molded package.
FIG. 5 illustrates a diagrammatic sectional view of the latter package wherein reference numerals 10 and 12 denote a lead frame and a molded body, respectively. This package is provided as a package in which the lead frame 10 is integral with the molded body 12. A semiconductor chip 16 is mounted in a recessed chip-mounting area 14, and electrically connected to the lead frame 10 by wires 18. Then, the chip-mounting area 14 is covered by a lid 20 which is bonded with an adhesive 25 to shield the semiconductor chip 16. The resultant assembly is used as a DIP type or gull-wing type semiconductor device.
The prior art package wherein the lead frame is used, however, has the following problems:
Although the package of this type is simple in structure, it necessitates a process for removing a dam bar (not shown) which is provided for preventing resin from flowing into the spaces between adjacent leads, after the molded body 12 has been molded by a transfer or injection molding process, and further removing resinous flash flowing into spaces between adjacent lead portions extending to the dam bar as in a conventional resin-shield type semiconductor device. This makes the production thereof troublesome.
In addition, a die for cutting the dam bar is expensive and requires a long manufacturing time to result in the increase of the package production cost.
Also, while external leads 10b must be subjected to a forming process to be of a DIP type or a gull-wing type, a die used for such forming is expensive, which is one of factors of the increase of package production cost.
When handling the package for the purpose, for example, of transportation after the external leads 10b have been formed to have a predetermined shape, the external lead 10b is liable to deform because it is supported in a cantilever manner, which is one of factors in a short-circuit accident.
Further, since the external leads 10b extend outward from a body of the package, a total size of the package becomes larger by the length of the external leads 10b, which does not satisfy the requirement for compactness.
On the other hand, a semiconductor device is disclosed in a prior patent application of the present Applicant (Japanese Unexamined Patent Publication No. 5-283460), wherein a base film 50 provided with circuit patterns (lead patterns 52) on the upper surface of a film-like resin substrate is used for compacting the package. That is, as shown in FIG. 6, the lead patterns 52 are provided on the upper surface of the insulating base film 50 and through-holes 54 are provided in the base film 50 so that intermediate portions of the lead pattern 52 are exposed from the base film 50, wherein solder bumps 56 are formed to be projected downward from the exposed lead patterns 52 through the base film 50. Thereby, it is possible to connect the lead patterns 52 with connector pads on the substrate via the solder bumps 56 without the external leads. Thus, the semiconductor device can be smaller in size.
This prior art invention, however, has been made on the premise that the base film 50 is used and the resin-molding is not carried out, which means that a lead frame and a resin-molding technology capable of forming desirable circuit patterns in a stable manner at a lower cost is not usable.
An object of the present invention is to provide a premold type package for a semiconductor device and a process for producing the same, wherein a lead frame is suitably used so that the package is easily and reliably produced in a stable manner at a lower manufacturing cost.
Another object of the present invention is to solve the above-mentioned problems in the prior art under such circumstances.
According to the present invention, there is provided a premold type semiconductor package comprising: a plurality of leads arranged side by side and having first and second common surfaces; a mold resin integrally molded with the leads for securing them from the first and second surfaces thereof; the mold resin defining a chip mounting recess at a first side on the first surfaces of the leads, so that a semiconductor chip is to be mounted in the recess; the first surfaces of the leads being partially exposed in the recess so as to define internal connecting terminals to which the semiconductor chip is to be electrically connected; and the mold resin provided with a plurality of holes by which the second surfaces of the leads are partially exposed to define external connecting terminals.
The mold resin has substantially a rectangular shape and the chip mounting recess is located at a central area of the mold resin at the first side thereof. Each of the leads extends from an outer periphery of the mold resin to the recess so that the first surface of the lead is exposed at an inner end thereof in the recess.
An outer end of the lead is covered with electrically insulating material.
A stage, made of same material as the leads and on which a semiconductor chip is to be mounted, is provided at a central area of the chip mounting recess, so that the inner end of the leads are arranged adjacent to a periphery of the stage.
Each of the holes has a tapered shape, a diameter thereof being gradually increased toward a surface of the mold resin.
Dach of the holes is filled with electrically conducting material to contact with the external connecting terminal to define an external connecting bump.
According to another aspect of the present invention, there is provided a process for manufacturing a premold type semiconductor package comprising the following steps of:
inserting a lead frame between first and second molds at their open position, the first and second molds having recesses which cooperatingly define a cavity therebetween when they are in their closed position, the first mold having a protruded portion which is in contact with a first surface of the lead frame in a closed position, and the second mold having a plurality of pins projected into the cavity, the pins being in contact with a second surface of the lead frame in the closed position;
bringing the first and second molds to their closed position so that the lead frame is nipped therebetween;
injecting resin into the cavity to form a mold resin integrally molded with the leads; and
cutting respective leads of the lead frame extending outward from the mold resin;
whereby obtaining a package comprising: a plurality of leads cut off from the lead frame, the mold resin integrally molded with the leads, the mold resin defining a chip mounting recess on first surfaces of the leads formed by the protruded portion and provided with a plurality of holes formed by the plurality of pins to define external connecting terminals of the leads.
A step may further comprise: forming bumps on the external connecting terminals by filling the plurality of holes with electrically conducting material.
A step may further comprise: covering outer ends of the leads with electrically insulating material.
Each of the pins is a tapered pin so that the hole of the package has a tapered shape, a diameter thereof being gradually increased toward a surface of the mold resin.